Potassium Flashcards
Cellular functions of K+:
protein and glycogen synthesis
Normal extracellular K+:
4-5 meq/L
Electrical function of K+:
maintains resting membrane potential
Sx of low or high K+:
cramps
muscle weakness/paralysis
EKG changes/arrhythmias
**relates to the inability of muscles to generate action potentials
EKG changes in hyp-O-kalemia:
PR prolongation
ST depression
flattened or inverted T wave
U waves (right after T wave)
QRS widening
EKG changes in hyp-ER-kalemia:
PR prolongation
ELEVATED T waves
widened QRS
What increases threshhold potential and protects against the decreased resting potential of hyp-ER-kalemia?
hypercalcemia
Releases K+ from cells in exchange for HCl buffering, exacerbating hyperkalemia?
metabolic acidosis
Hypokalemia _______ digoxin toxicity but hyperkalemia ______ digoxin toxicity.
increases
causes
Molecules that move K+ into cells:
insulin
catecholamines
How do insulin and catecholamines get K+ into cells?
increased activity of Na-K-ATPase
increase uptake in skeletal muscle and liver
Acidemia effect on serum K+:
Increases as H+ is buufered in to cells
Alkalemia effect on serum K+:
Decrease as H+ is buffered into extracellular fluid
If K+ lost in stool or sweat is clinically relevant?
Pathologic
Major route of K+ elim?
Kidney
Determinants of K+ secretion by kidney:
plasma concentration
urine flow in distal tubule
ALDOSTERONE: K+ secretion by PRINCIPAL cells of collecting tubule
How does K+ get reabsorbed in loop of Henle?
NKCC pump
How can K+ get reabsorbed during severe hypokalemia?
Intercalated cells in collecting tubule
alpha cells – K+/H+ antiporter
Distal tubule secretion of K+ involves?
Principal cells
- luminal Na+ and K+ channels
- basolateral Na-K-ATPase
ALDOSTERONE
- very sensitive to K+ change (responds to 0.1 meq increase)
- increases Na and K channels
- increases activity of NA-K-ATPase
K conc gradient
distal flow is permissive??
Causes of hyp-O-kalemia:
decreased intake (rare)
increased entry into cells (acidemia)
increased GI loss
increased urinary loss
increased sweat loss
dialysis
Dietary phenomena that binds K+ leading to hypokalemia?
Clay ingestion
Three causes of hypokalemia due to increased cellular uptake:
metabolic acidosis
hyperinsulinemia
increased catecholamines
Causes of hypokalemia due to increased urinary loss?
Increased distal flow due to impaired salt and water reabsorption
- diuretics
- salt wasting nephropathies
- polydypsia/polyuria
Hypercalcemia
Mineral corticoid excess (Aldosterone)
Hypomagnesemia (effects K channels)
How would you determine if K loss was due to kidney?
24 hour urine K+ test
if low –> not kidney problem
If you have a low urinary K (GI loss) and acidemia, what part of GI tract is responsible?
Lower GI (laxatives, cancer)
If low urinary K (GI loss) and alkalemia, what part of GI tract is responsible?
Upper (vomiting)
If K loss is kidney related with acidemia, what are the possible problems?
ketoacidosis
type I or II renal tubular acidosis
If K loss is kidney related and alkalemia is present in a normotensive patient, what could the problem be?
vomiting
diuretics (early)
Bartter’s syndrome (inherited)
Hypertensive alkalosis due to kidney loss of K with high renin could be from:
diuretics
renovascular disease
reninoma
Cushings
Hypertensive alkalosis due to kidney loss of K with low renin could be from:
low aldosterone (or high???)
Drugs that can cause hyperkalemia in the setting of normal total body K:
succinylcholine
beta blockers
digoxin
Most common cause of hyperkalemia:
renal failure
Major hormone responsible for renal excretion of K?
Aldosterone
First thing to do to treat hyperkalemia?
Calcium IV
Second things to do to get K into cells in Hyperkalemia?
Glucose and insulin
NaHCO3
Beta-agonist (albuterol nebs)
3% NaCl if hyponatremic
Long term(ish) treatment (hours) for hyperkalemia:
loop diuretics
cation exchange (kayexalate)
dialysis
